Make a trait out of sign::StateMachine for more complex Transaction flows

coins/monero/tests/clsag.rs

@@ -7,7 +7,7 @@ use monero_serai::{random_scalar, Commitment, frost::MultisigError, key_image, c
 #[cfg(feature = "multisig")]
 mod frost;
 #[cfg(feature = "multisig")]
-use crate::frost::{generate_keys, sign};
+use crate::frost::{THRESHOLD, generate_keys, sign};
 
 const RING_INDEX: u8 = 3;
 const RING_LEN: u64 = 11;
@@ -86,17 +86,21 @@ fn test_multisig() -> Result<(), MultisigError> {
     ring.push([&dest * &ED25519_BASEPOINT_TABLE, Commitment::new(mask, amount).calculate()]);
   }
 
-  let mut algorithms = Vec::with_capacity(t);
-  for _ in 1 ..= t {
-    algorithms.push(
-      clsag::InputMultisig::new(
-        clsag::Input::new(ring.clone(), RING_INDEX, Commitment::new(randomness, AMOUNT)).unwrap(),
-        Msg(msg)
+  let mut machines = Vec::with_capacity(t);
+  for i in 1 ..= t {
+    machines.push(
+      sign::AlgorithmMachine::new(
+        clsag::InputMultisig::new(
+          clsag::Input::new(ring.clone(), RING_INDEX, Commitment::new(randomness, AMOUNT)).unwrap(),
+          Msg(msg)
+        ).unwrap(),
+        keys[i - 1].clone(),
+        &(1 ..= THRESHOLD).collect::<Vec<usize>>()
       ).unwrap()
     );
   }
 
-  let mut signatures = sign(algorithms, keys);
+  let mut signatures = sign(&mut machines, keys);
   let signature = signatures.swap_remove(0);
   for s in 0 .. (t - 1) {
     // Verify the commitments and the non-decoy s scalar are identical to every other signature

coins/monero/tests/frost.rs

@@ -8,7 +8,7 @@ use rand::rngs::OsRng;
 use ff::Field;
 use dalek_ff_group::{ED25519_BASEPOINT_TABLE, Scalar, EdwardsPoint};
 
-use frost::{
+pub use frost::{
   FrostError, MultisigParams, MultisigKeys,
   key_gen, algorithm::Algorithm, sign::{self, lagrange}
 };
@@ -113,26 +113,16 @@ pub fn generate_keys() -> (Vec<Rc<MultisigKeys<Ed25519>>>, Scalar) {
 }
 
 #[allow(dead_code)] // Currently has some false positive
-pub fn sign<S, A: Algorithm<Ed25519, Signature = S>>(
-  algorithms: Vec<A>,
+pub fn sign<S, M: sign::StateMachine<Signature = S>>(
+  machines: &mut Vec<M>,
   keys: Vec<Rc<MultisigKeys<Ed25519>>>
 ) -> Vec<S> {
-  assert!(algorithms.len() >= THRESHOLD);
-  assert!(keys.len() >= algorithms.len());
+  assert!(machines.len() >= THRESHOLD);
+  assert!(keys.len() >= machines.len());
 
-  let mut machines = vec![];
   let mut commitments = Vec::with_capacity(PARTICIPANTS + 1);
   commitments.resize(PARTICIPANTS + 1, None);
   for i in 1 ..= THRESHOLD {
-    machines.push(
-      sign::StateMachine::new(
-        sign::Params::new(
-          algorithms[i - 1].clone(),
-          keys[i - 1].clone(),
-          &(1 ..= THRESHOLD).collect::<Vec<usize>>()
-        ).unwrap()
-      )
-    );
     commitments[i] = Some(machines[i - 1].preprocess(&mut OsRng).unwrap());
   }
 

sign/frost/src/sign.rs

@@ -65,6 +65,7 @@ pub struct Params<C: Curve, A: Algorithm<C>> {
   view: ParamsView<C>,
 }
 
+// Currently public to enable more complex operations as desired, yet solely used in testing
 impl<C: Curve, A: Algorithm<C>> Params<C, A> {
   pub fn new(
     algorithm: A,
@@ -400,30 +401,70 @@ impl fmt::Display for State {
   }
 }
 
-/// State machine which manages signing
+pub trait StateMachine {
+  type Signature;
+
+  /// Perform the preprocessing round required in order to sign
+  /// Returns a byte vector which must be transmitted to all parties selected for this signing
+  /// process, over an authenticated channel
+  fn preprocess<R: RngCore + CryptoRng>(
+    &mut self,
+    rng: &mut R
+  ) -> Result<Vec<u8>, FrostError>;
+
+  /// Sign a message
+  /// Takes in the participant's commitments, which are expected to be in a Vec where participant
+  /// index = Vec index. None is expected at index 0 to allow for this. None is also expected at
+  /// index i which is locally handled. Returns a byte vector representing a share of the signature
+  /// for every other participant to receive, over an authenticated channel
+  fn sign(
+    &mut self,
+    commitments: &[Option<Vec<u8>>],
+    msg: &[u8],
+  ) -> Result<Vec<u8>, FrostError>;
+
+  /// Complete signing
+  /// Takes in everyone elses' shares submitted to us as a Vec, expecting participant index =
+  /// Vec index with None at index 0 and index i. Returns a byte vector representing the serialized
+  /// signature
+  fn complete(&mut self, shares: &[Option<Vec<u8>>]) -> Result<Self::Signature, FrostError>;
+
+  fn multisig_params(&self) -> MultisigParams;
+
+  fn state(&self) -> State;
+}
+
+/// State machine which manages signing for an arbitrary signature algorithm
 #[allow(non_snake_case)]
-pub struct StateMachine<C: Curve, A: Algorithm<C>> {
+pub struct AlgorithmMachine<C: Curve, A: Algorithm<C>> {
   params: Params<C, A>,
   state: State,
   preprocess: Option<PreprocessPackage<C>>,
   sign: Option<Package<C>>,
 }
 
-impl<C: Curve, A: Algorithm<C>> StateMachine<C, A> {
+impl<C: Curve, A: Algorithm<C>> AlgorithmMachine<C, A> {
   /// Creates a new machine to generate a key for the specified curve in the specified multisig
-  pub fn new(params: Params<C, A>) -> StateMachine<C, A> {
-    StateMachine {
-      params,
-      state: State::Fresh,
-      preprocess: None,
-      sign: None,
-    }
+  pub fn new(
+    algorithm: A,
+    keys: Rc<MultisigKeys<C>>,
+    included: &[usize],
+  ) -> Result<AlgorithmMachine<C, A>, FrostError> {
+    Ok(
+      AlgorithmMachine {
+        params: Params::new(algorithm, keys, included)?,
+        state: State::Fresh,
+        preprocess: None,
+        sign: None,
+      }
+    )
   }
+}
 
-  /// Perform the preprocessing round required in order to sign
-  /// Returns a byte vector which must be transmitted to all parties selected for this signing
-  /// process, over an authenticated channel
-  pub fn preprocess<R: RngCore + CryptoRng>(
+impl<C: Curve, A: Algorithm<C>> StateMachine for AlgorithmMachine<C, A> {
+  type Signature = A::Signature;
+
+  fn preprocess<R: RngCore + CryptoRng>(
     &mut self,
     rng: &mut R
   ) -> Result<Vec<u8>, FrostError> {
@@ -437,12 +478,7 @@ impl<C: Curve, A: Algorithm<C>> StateMachine<C, A> {
     Ok(serialized)
   }
 
-  /// Sign a message
-  /// Takes in the participant's commitments, which are expected to be in a Vec where participant
-  /// index = Vec index. None is expected at index 0 to allow for this. None is also expected at
-  /// index i which is locally handled. Returns a byte vector representing a share of the signature
-  /// for every other participant to receive, over an authenticated channel
-  pub fn sign(
+  fn sign(
     &mut self,
     commitments: &[Option<Vec<u8>>],
     msg: &[u8],
@@ -463,11 +499,7 @@ impl<C: Curve, A: Algorithm<C>> StateMachine<C, A> {
     Ok(serialized)
   }
 
-  /// Complete signing
-  /// Takes in everyone elses' shares submitted to us as a Vec, expecting participant index =
-  /// Vec index with None at index 0 and index i. Returns a byte vector representing the serialized
-  /// signature
-  pub fn complete(&mut self, shares: &[Option<Vec<u8>>]) -> Result<A::Signature, FrostError> {
+  fn complete(&mut self, shares: &[Option<Vec<u8>>]) -> Result<A::Signature, FrostError> {
     if self.state != State::Signed {
       Err(FrostError::InvalidSignTransition(State::Signed, self.state))?;
     }
@@ -482,11 +514,11 @@ impl<C: Curve, A: Algorithm<C>> StateMachine<C, A> {
     Ok(signature)
   }
 
-  pub fn multisig_params(&self) -> MultisigParams {
+  fn multisig_params(&self) -> MultisigParams {
     self.params.multisig_params().clone()
   }
 
-  pub fn state(&self) -> State {
+  fn state(&self) -> State {
     self.state
   }
 }

sign/frost/tests/key_gen_and_sign.rs

@@ -10,7 +10,7 @@ use frost::{
   MultisigParams, MultisigKeys,
   key_gen,
   algorithm::{Algorithm, Schnorr, SchnorrSignature},
-  sign
+  sign::{StateMachine, AlgorithmMachine}
 };
 
 mod common;
@@ -28,13 +28,11 @@ fn sign<C: Curve, A: Algorithm<C, Signature = SchnorrSignature<C>>>(
   commitments.resize(PARTICIPANTS + 1, None);
   for i in 1 ..= t {
     machines.push(
-      sign::StateMachine::new(
-        sign::Params::new(
-          algorithm.clone(),
-          keys[i - 1].clone(),
-          &(1 ..= t).collect::<Vec<usize>>()
-        ).unwrap()
-      )
+      AlgorithmMachine::new(
+        algorithm.clone(),
+        keys[i - 1].clone(),
+        &(1 ..= t).collect::<Vec<usize>>()
+      ).unwrap()
     );
     commitments[i] = Some(machines[i - 1].preprocess(&mut OsRng).unwrap());
   }